1. Field of the Invention
The present invention relates generally to avionics systems and more particularly to improved switching systems for Avionics Full-Duplex Switched Ethernet (AFDX) systems.
2. Description of the Related Art
Modern onboard avionics networks serve to provide data transfer between various components of an aircraft. Avionics systems typically have a variety of systems that provide data to processing components of the aircraft or exchange data among one or more components of the aircraft. For example, a variety of avionics modules may gather avionics data (e.g., sensors detecting speed, direction, external temperature, control surface positions, and the like) that is routed by the avionics system via an avionics network to one or more aircraft components such as displays, monitoring circuits, processors, and the like.
In some aircraft systems, the avionics network may be constructed with an Aeronautical Radio Inc. (ARINC) 429 data bus capable of supporting communication between many components. More recently, Ethernet networks have been used in avionic network environments by leveraging Commercial Off-The-Shelf (COTS) technology to increase bandwidth and reduce cost.
Ethernet type networks have been used in communication networks for implementing communication among various network components. An Ethernet network may be used to send or route data in a digital form by packets or frames. Each packet contains a set of data, and the packet is generally not interpreted while sent through the Ethernet network. In an avionics network environment, the Ethernet network typically has different components that subscribe to the avionics network and connect to each other through switches. Each network subscriber can send packets in digital form, at controlled rates, to one or more other subscribers. When a switch receives the packets, the switch determines the destination equipment and directs or switches the packets to such equipment.
Such Ethernet networks may include ARINC-664 based networks. In a switched full-duplex Ethernet type network, the term “full-duplex” refers to sending and receiving packets at the same time on the same link, and the term “switched” refers to the packets being switched in switches on appropriate outputs. However, the ARINC-664 network uses multiple switches and redundant paths to route data, point-to-point or point-to-multipoint across the switches.
Avionics Full-Duplex Switched Ethernet (AFDX) is a data network for safety-critical applications that utilizes dedicated bandwidth while providing deterministic Quality of Service (QoS). AFDX is based on IEEE 802.3 Ethernet technology and utilizes Commercial Off-The-Shelf (COTS) components. AFDX is a specific implementation of ARINC Specification 664 Part 7, a profiled version of an IEEE 802.3 network per parts 1 & 2, which defines how Commercial Off-the-Shelf networking components will be used for future generation Aircraft Data Networks (ADN). The six primary aspects of AFDX include full duplex, redundancy, deterministic, high speed performance, switched and profiled network.
Certain AFDX data networks require synchronous scheduling for proper operation. For example, U.S. Pat. No. 7,675,919, issued to S. C. Vestal, entitled, “End System Scheduling for Switched Networks,” discloses a method for scheduling one or more data packet transfers over a computer-based distributed network. The method involves constructing a cyclic schedule from a plurality of data packets, wherein the cyclic schedule is constructed to ensure that each data packet transfer is substantially free of jitter. The method further involves synchronizing the cyclic schedule with at least one periodic processing schedule and transmitting the synchronized data packets as arranged by the cyclic schedule.
U.S. Pat. No. 7,787,486, issued to S. C. Vestal, entitled, “Method and System for Achieving Low Jitter in Real-Time Switched Networks,” discloses a method and system for increasing the precision of time synchronization among a plurality of host nodes in a packet-switched network by reducing transmission delay variation in the network. Each host node is provided with a distinct set of transmission times selected from a global schedule in such a way as to avoid concurrent transmission of messages by the plurality of host nodes. The transmission times may be determined as offsets within a global hyperperiod, and each host node carries out transmissions according to predetermined offsets of the respective host node. Transmissions according to offsets may be applied to real-time messages, including time-synchronization messages, hence yielding increased precision of synchronization.
Some networks are designed for asynchronous operation between components. This provides cost savings. With such networks each end system is viewed as having a set of flows where each flow has an expected arrival envelope. It is desired that the number of virtual links (VLs) be maximized for a given level of performance.
In conventional networks, delay-jitter along the propagation path grows exponentially as each flow propagates from switch to switch and as the number of virtual flows grows. As will be disclosed below, with the present invention delay-jitter is eliminated for all but the final switch in an AFDX network. This implies that the delay-jitter experienced for end systems connected to the same switch is nearly the same as for those connected to another switch using an AFDX switching trunk line. Delay-jitter management remains an important issue for avionics systems and it is desired to minimize such delay-jitter.
Circular Dependence occurs when one or more flows have no defined traffic envelope at a given output port. This problem is very easily generated in an aircraft as each function is duplicated for availability. Function X and Y are implemented as X, X′, Y and Y′ with full interconnectivity provided. In fact circular dependence must be proactively avoided, affecting the routing choices of VLs in the network.
An example of a system for avoiding circular dependence is disclosed in U.S. Pat. No. 7,983,195, issued to Andreoletti, et al., entitled, “Method of Routing Virtual Links in a Frame-Switching Network With Guaranteed Determinism.” The '195 patent discloses a method for routing virtual links in a frame switching network including a plurality of source terminals and/or destination of the frames, frame switches being connected together through physical connections, each virtual link being defined, for a point-to-point type, by a path through the network between a source terminal and a destination terminal and, for a multipoint type, by a plurality of paths through the network between a source terminal and a plurality of destination terminals. The method carries out routing of the links while observing a segregation constraint with regard to triplets of consecutive switches belonging to the oriented loops, so as to allow verification of determinism of the network. However, it constrains the flow routing making the process more complex.
As will be disclosed below the present invention addresses four issues relating to the AFDX switching performance and analysis: First, the end-to-end delay bound computation complexity. Second the vulnerability of AFDX to VL routing induced circular dependence. Third, the introduction of delay-jitter at intermediate AFDX switches in the network. Fourth, end systems measures needed to very precisely compute the transmission time of each frame in order to limit the delay-jitter experienced by the flow and the impact on the system. Fifth, the avoidance of having to use static priority packet scheduling.
U.S. Ser. No. 13/533,034, now issued as U.S. Pat. No. 8,817,622, entitled, “DATA NETWORK WITH AGGREGATE FLOW MONITORING,” filed concurrently herewith, by the applicants, D. A. Miller and D. E. Mazuk, and assigned to the present assignee, discusses the use of aggregate flow monitoring in a data network for monitoring the aggregate arrival data flow in defined traffic constraint envelopes containing frames. This co-filed patent application is incorporated by reference herein in its entirety.
U.S. Ser. No. 13/533,265, entitled, “DATA NETWORK WITH CONSTRAINED SWITCH TRANSMISSION RATES,” filed concurrently herewith, by the applicant, D. A. Miller, and assigned to the present assignee, discusses a data network utilizing packet schedulers for managing the transmission of received data flow. A plurality of effective line rate utilization mechanisms are each associated with a respective packet scheduler for providing the service rate of that packet scheduler. A plurality of switch egress ports transmit the received data flow. Each switch egress port has a defined configured effective transmission rate. Each effective line rate utilization mechanism reduces the utilization rate to the defined configured effective transmission rate. This co-filed patent application is incorporated by reference herein in its entirety.